What Causes Cough After Taking Lisinopril?

My friend was taking 20mg lisinopril. Developed the cough after taking it and today doctor switched him to 100mg losartan. We know these are 2 different meds, however, it just seems there s a huge difference in mg. His bp at doctors office was 120/85. He has a very strict diet and is at appropriate weight. We actually were thinking maybe the lisinopril would be reduced because he has done extremely well since November 2016 with bp. Height 6 3 , Weight 180, Age 56 Bp problem developed after wife was in a horrific car accident and almost died. This was 3 years ago. She is unable to stay at home and is a nursing home. He visits her 6 out of 7 days weekly and also works 6 days a week.